1. Field of the Invention
This invention relates to the field of pattern generation using a laser and radiant sensitive film, in particular for the fabrication of integrated circuits.
2. Prior Art
In the photolithographic fabrication of integrated circuits, film sensitive to radiant particle energy is exposed in predetermined patterns to define circuit features. In some cases, the energy is passed through masks which contains the patterns, thereby selectively exposing a photoresist film on a semiconductor body. In other instances, the film is on a mask substrate and the film is exposed as a step in the making of the mask. Other times the direction of the radiant energy itself is controlled to define patterns in the film. This can be done as part of the making a mask (or reticle) or to directly "write" onto the resist film covering a semiconductor wafer. Several sources of radiant energy have been used, including ultraviolet light, visible light, coherent light, x-rays and electron beam (E-Beam).
A system for photolithographic fabrication of integrated circuits is described in U.S. Pat. No. 4,796,038 entitled "Laser Pattern Generation Apparatus" which is assigned to the assignee of the present application. In U.S. Pat. No. 4,796,038 circuit patterns are written onto a workpiece by directing laser beams and moving a workpiece relative to the laser beams. A single laser beam is split into eight (8) beams to form a brush. The beams pass through a multi-channel Acousto-Optical Modulator (AOM). The AOM receives electric signals defining the circuit patterns. The AOM is used to control the intensity of the beams as they write onto the workpiece. A steering mirror is used for directing the plurality of beams through a zoom lens arrangement and towards a rotating polygonal mirror. The steering mirror is used to adjust and align the beams in response to movement of the workpiece. The zoom lens arrangement is for adjusting the size and placement of the beams. The rotating polygonal mirror has a plurality of facets and is used to scan the beams onto the workpiece in a raster-like scan. Through successive scans of the brush, a stripe is printed on the workpiece. The stripes comprise the different portions of the integrated circuit pattern.
Commercially available systems embodying the laser pattern generation apparatus of U.S. Pat. No. 4,796,038 include the CORE 2100, 2500, 2564 and WAFER WRITE-6000 Systems available from Etec Systems, Inc. of Beaverton, Oreg.
Although the laser pattern generation apparatus of U.S. Pat. No. 4,796,038 and the commercially available embodiments provide satisfactory results, increased printing speed is always desirable. Thus, it is a primary object of the present invention to increase printing speed. Furthermore, this increase in speed can be used to reduce pattern errors through further use of multi-pass averaging.
Known laser based pattern generation apparatus of this type have other limitations. One such limitation concerns laser alignment. Laser alignment is critical. Variations in laser alignment introduces various errors in the printing process, resulting in incorrectly generated patterns. The direction and resulting alignment of a laser beam is affected by the temperature of the laser. Typically, the laser is water cooled. Thus, variations in the water temperature may have an effect on the alignment of the laser beam. Such systems have water temperature control sensors which monitor and maintain control of the water temperature to within a narrow range, (e.g. 0.1.degree. Celsius). Such temperature control systems add complexity to the pattern generation apparatus. It would be desirable to have an apparatus where water control temperature need not be so precisely maintained.
Further, adjusting laser beam alignment is a manual process that requires significant down-time of the apparatus. It would be desirable to provide an apparatus wherein laser beam alignment may be corrected so as to minimize the amount of required down-time.
Other improvements over the prior art systems will become apparent in the description of the present invention.